Background of the invention.
Description of the related art.
Manual, diver-assisted metrology.
ROV-assisted metrology.
An overview of embodiments of the invention in a general context.
I: A xe2x80x9cfull Smartwirexe2x80x9d device embodiment.
II: A xe2x80x9cfull Smartwirexe2x80x9d method embodiment.
III: A xe2x80x9clightxe2x80x9d Smartwire device embodiment.
IV: A xe2x80x9cmappingxe2x80x9d method embodiment.
V: A xe2x80x9cpositioningxe2x80x9d method embodiment.
Summary of the invention.
Brief description of the drawings.
Specification of a preferred embodiment of the invention, (with reference numerals referring to the drawings and the set of claims).
III: A xe2x80x9clightxe2x80x9d-Smartwire device embodiment.
II: A xe2x80x9cSmartwirexe2x80x9d method embodiment.
I: A xe2x80x9cfullxe2x80x9d Smartwire device embodiment.
The subsea operation using the full device.
IV: A xe2x80x9cmappingxe2x80x9d method embodiment.
V: A xe2x80x9cpositioningxe2x80x9d method embodiment.
Mathematical outline of the metrology calculations.
Computer implementation
Robustness of measurements.
Displacement along the pipe or hub.
Multiple hubs on a manifold.
Claims.
Abstract.
1. Field of the Invention
This invention relates to an ROV-supported metrology device and a method for precision measurements of relative position and orientation of two or more objects (connection points) at the seabed, e.g. measuring distance and relative orientation of two pipe terminations subsea; two pipe flanges which are to be connected. To give an example, pipelines which are laid out ready on the seabed, shall be connected to a subsea manifold which becomes lowered to the seabed in a separate operation, see FIG. 2. The manifold has pipeline receptors/hubs which are to be connected with the pipeline terminations via hard-piped so-called tie-in jumpers or spoolpieces. The position for the manifold on the seabed must be within a predefined area, but it is infeasible to predetermine this position precisely enough to allow for rigid prefabricated jumper spools made in steel. The pipelines shall be connected to the manifold""s hubs via hard-piped jumper spools which must be tailored according to the local separations and relative orientations. Installation of flexible jumpers are not considered.
2. Description of the Related Art
Manual, Diver-assisted Metrology
Manual equipment for metrology of manifold and pipeline relative orientation and separation exists. Such measurements are made by divers on the site and later reproduced using the same equipment in a jig at a surface vessel or onshore. End pieces with the desired orientation and separation are arranged in the jig, and then a jumper spool is welded to the end pieces and tested. Thereafter the jumper spoolpiece is lowered down and placed between the manifold and the pipeline, and connected.
Disadvantages of Manual Metrology
Manual metrology performed by divers is inaccurate, time-consuming and expensive. Diver assistance is not feasible for the entire depth range considered, often more than 300 meters, down to more than 1500 meters. Generally, the use of diver assistance may be discouraged due to the general health hazard connected with offshore diving.
ROV-assisted Metrology
A system for ROV-assisted diverless metrology of subsea installations and subsequent hard-piping connection between a production manifold and pipelines, is described in Offshore Technology Conference, 1996: OTC 8134: Sanjay K. Reddy et al: xe2x80x9cDiverless Hard-Pipe Connection Systems for Subsea Pipelines and Flowlinesxe2x80x9d. The measurement system xe2x80x9cPre-Measurement Toolxe2x80x9d, PMT, comprises a xe2x80x9cMeasurement Toolxe2x80x9d, MT, with a landing/alignment pin arranged for a measurement receptacle on the termination to be measured. The MT is provided with a length metering cable, two inclinometers and horizontal and vertical angle readouts for the taut-cable orientation. A xe2x80x9cMeasurement Pinxe2x80x9d, MP, with a landing pin arranged for a receptacle on the other termination to be measured is to be connected via the cable, all shown in FIGS. 5 and 10 of the article OTC 8134. The cable is drawn from the MT and hooked onto the MP by means of an ROV. The ROV then reads off the horizontal relative azimuth and vertical inclination of the cable relative to the MT. The ROV camera must be moved into position to view the inclinometers of the MT. The reading of the scales is conducted by an operator on the surface via the ROV camera.
Disadvantages of the Known ROV Metrology
The camera reading procedure is a separate source of error, as a parallax error will arise because of the orientation between the ROV camera and the scales to be viewed. Another problem with the existing diverless system is the time-consuming ROV-manoevering procedure to get the camera in position for reading off the angles. This measuring must be conducted at both terminations, thus doubling the effort of measuring the orientation of the two separations. The readings are, as with the diver-assisted method, mimicked at the surface in a xe2x80x9cmanifold end/pipeline end construction jigxe2x80x9d having receptacles at either end for the PMT tools MT and MP, and height and inclination adjustment for the receptacles. Jumper spool endpieces are then mounted at either receptacle and a spool pipe with the desired length and orientation is then welded between the jumper spool endpieces sitting in the construction jig. The resulting jumper spoolpiece is then lowered and connected accordingly.
In addition to the parallax problems, another problem has been described as inconsistent pull force of the PMT tool, a pull which depends on the ROV hot stab pressure.
Thus it is desirable to have a system which overcomes the inaccuracy of reading the angles.
It is desirable to have a metrology system which overcomes the slow measurement procedure of the existing systems. It is also highly desirable to have a method and a device being independent of divers. It is also desirable to have a metrology system being independent of the the pull force of the hot stab of the ROV.
In addition, it is desirable to have a metrology system also being capable of conducting local mapping of the seabed and structures around a local reference system defined by e.g. a manifold frame which has been arranged at the seabed. It is equally desirable to have a system being capable of setting out markers, e.g. marker buoys, for indicating the future position for equipment which shall be arranged at the seabed in a reference system being relative to e.g. a manifold frame at the seabed. Arranging passive markers at the seabed according to one method of the invention eliminates the need for maintenance of transponder arrays.
The existing system requires that the wire is extended between two receptacle points before the angles are measured. The existing system is not capable of being used for determining positions on the seabed relative to one existing receptacle at e.g. a manifold""s termination without having a first ROV to hold and tension the wire, and a second ROV to read off the angles at the receptacle""s end of the wire. Thus it is desirable to have a metrology system capable of mapping and determining positions on the seabed relative to one existing receptacle at e.g. a manifold termination in one single tensioning-and-measuring operation with one single ROV.
The invention is embodied both in a device and several methods for subsea metrology. There are several modes of operating different preferred embodiments of the invention:
I: A xe2x80x9cfull Smartwirexe2x80x9d device embodiment;
II: A xe2x80x9cSmartwirexe2x80x9d method embodiment;
III: A xe2x80x9clightxe2x80x9d Smartwire device embodiment;
IV: A xe2x80x9cmappingxe2x80x9d method embodiment.
V: A xe2x80x9cpositioningxe2x80x9d method embodiment.
A xe2x80x9cfull Smartwirexe2x80x9d device and Smartwire method embodiment of the invention may be described with reference to FIG. 1c and FIG. 1e: An ROV may generally carry two metrology units. A so-called xe2x80x9creferencexe2x80x9d metrology unit is attatched to e.g. a manifold""s (or a pipeline""s) termination, e.g. a hub. A so-called xe2x80x9cbasexe2x80x9d metrology unit is carried to a basically independent pipeline termination, normally a flange, and attached to that pipeline termination, by the ROV. The ROV will be controlled to attach the metrology units with their base-planes preferreably being close to the true horizontal plane. A wire is connectng the two metrology units, and is tensioned. Several measurements are conducted by the two metrology units:
The length of the taut wire, preferrably by the tensioning metrology unit,
the depth of submergence of the base metrology unit (on the manifold termination),
the entry angle of the taut wire as projected in a generally horizontal plane on the base metrology unit,
the depth of submergence of the reference metrology unit (on the pipeline termination),
the entry angle of the taut wire as projected in a generally horizontal plane on the reference metrology unit,
in a preferred embodiment, the base metrology unit""s deviation angles from the true horizontal, and
in a preferred embodiment, the reference metrology unit""s deviation angles from the true horizontal.
The measurements conducted by the reference unit at the end of the extendable wire are transferred to the base unit and preferrably to the ROV. The distance and the relative orientations of the units are then calculated on the basis of the above mentioned measurements. The measurements may be stored and post-processed by the ROV""s re-emergence to the surface, but according to a most preferred embodiment, the invention is tailor-made for offshore use as follows: An algorithm for a metrology process is arranged for real-time calculation of the relative positions and to display data (illustrated in FIG. 5a) in data acquisition units at the surface (illustrated in FIGS. 4b and 5b). Relative positions and orientations of the two terminations are calculated, and may be transferred to a CAD/CAM unit to produce engineering drawings for production of tailor-made rigid jumper spoolpieces directly after the measurements have been conducted.
The taut wire""s angle is measured by means of a trailing arm with an angle encoder as displayed in FIG. 4a. In the described embodiment of the invention, only one horizontal wire angle encoder is employed at each metrology unit. This results in a more rugged device than a metrology device having both a horizontal angle encoder and a vertical angle encoder. It will be shown in a mathematical section that the measurements to be taken are sufficient for determining the relative positions and orientations of the two pipeline terminations.
A xe2x80x9clightxe2x80x9d Smartwire device embodiment of the invention is illustrated in FIG. 1a. The xe2x80x9clightxe2x80x9d Smartwire device comprises the following overall equipment: A metrology unit is carried by an ROV, playing both roles of xe2x80x9cbasexe2x80x9d and xe2x80x9creferencexe2x80x9d metrology units. The metrology unit is provided with an extendable wire. The extendable end of the wire is arranged to be attached to a dedicated receptacle at a separate manifold (or pipeline) xe2x80x9creferencexe2x80x9d termination. The metrology unit is arranged to be carried by the ROV to an independent pipeline xe2x80x9cbasexe2x80x9d termination and to attach it there. The wire is then tensioned. A first xe2x80x9cbasexe2x80x9d half set of measurements is then conducted by the metrology unit being in xe2x80x9cbasexe2x80x9d mode while attached at the pipeline xe2x80x9cbasexe2x80x9d termination:
The length of the taut wire,
the depth of submergence of the xe2x80x9cbasexe2x80x9d metrology unit,
the entry angle of the taut wire as projected in a generally horizontal plane on the xe2x80x9cbasexe2x80x9d metrology unit, and
in a preferred embodiment, the deviations of the xe2x80x9cbasexe2x80x9d metrology unit from the true horizontal.
After conducting the first xe2x80x9cbasexe2x80x9d half set of measurements, the arrangement of the extended wire and the metrology unit is reversed by means of the ROV, and a xe2x80x9creferencexe2x80x9d half set of measurements is conducted while the base metrology unit is attached at the opposite, xe2x80x9creferencexe2x80x9d manifold (or pipeline) termination to replicate the xe2x80x9cfullxe2x80x9d set of measurements:
(The length of the taut wire is the same)
the xe2x80x9creferencexe2x80x9d depth of submergence of the metrology unit,
the xe2x80x9creferencexe2x80x9d entry angle of the taut wire as projected in a generally horizontal plane on the metrology unit, and
in a preferred embodiment, the deviations of the xe2x80x9creferencexe2x80x9d metrology unit from the true horizontal.
The ROV will be controlled to attach the metrology unit with their base-planes preferreably being close to the true horizontal plane. In a preferred embodiment, orientation sensors in the metrology units will measure the deviations from the horizontal. The xe2x80x9clightxe2x80x9d embodiment takes longer to operate, but replicates through double effort the measurements taken by the xe2x80x9cfullxe2x80x9d embodiment, and thus forms a basis of the xe2x80x9cfullxe2x80x9d embodiment.
A xe2x80x9cmappingxe2x80x9d method embodiment is illustrated in FIG. 1d. The mapping method is in a preferred embodiment conducted using a device according to the xe2x80x9cfullxe2x80x9d embodiment using a xe2x80x9creferencexe2x80x9d metrology unit attached to a manifold (or pipeline) termination playing the role as a xe2x80x9creferencexe2x80x9d termination in a locally defined reference system for the mapping. A path comprised by points along the topography of the seabed is defined relative to the manifold""s termination. In the xe2x80x9conlinexe2x80x9d embodiment as described under point I/II with the full embodiment, successive relative positions of the base metrology unit may be displayed in real-time as the base metrology unit is moved from point to point at the seabed between the two terminations.
Combining in this way the method II with mapping of the seabed according to IV, a jumper spoolpiece may be tailored to the local seabed topography, having correctly oriented terminal connectors and being adapted to a desired degree to fit the local topography between the terminations.
A xe2x80x9cpositioningxe2x80x9d method embodiment is also illustrated in FIG. 1d, using the same device as described for the full version described above under point I. The xe2x80x9cpositioningxe2x80x9d method is conducted using basically the same devices as the xe2x80x9cmappingxe2x80x9d method, but may regarded as an inverse method to leave markers on the seabed. The markers define landing points for devices, or define new, intermediate, xe2x80x9cdead man""s anchorsxe2x80x9d having both position and orientation for extending the working range for the xe2x80x9cSmartwirexe2x80x9d metrology devices. The positioning method is in a preferred embodiment conducted using a device according to the xe2x80x9cfullxe2x80x9d embodiment using a xe2x80x9creferencexe2x80x9d metrology unit attached to a manifold""s termination defining a reference coordinate system for the positioning and planting of markers. Predetermined points having Cartesian or polar coordinates relative to the manifold""s reference coordinate system, and possibly a depth coordinate, are set out one by one at the seabed, and marked, e.g. by a marker buoy or the like. As in the xe2x80x9conlinexe2x80x9d embodiment as described above, the successive relative positions of the ROV carrying the marker buoys may be displayed in real-time as the ROV is moved from the manifold""s reference termination to the first point to leave a marker, and later to the successive marking points.
The above mentioned problems are overcome by a system with a device and a method according to the set of claims, comprising a device for subsea metrology of distance and relative orientation of two terminations, e.g. a manifold""s first termination which is to be connected to a pipeline""s second termination by means of a jumper spool pipe, the device comprising the following features:
A reference metrology unit arranged for aligned positioning at the first termination;
A base metrology unit;
A wire with its first, extendable end attached to a reference metrology unit, with a wire tensioner drum arranged on a base metrology unit for feeding out and tension the wire,and with a wire length sensor arranged to measure the length of the wire extending between the xe2x80x9creferencexe2x80x9d and the xe2x80x9cbasexe2x80x9d metrology units. The new features of the invention comprise:
A relative azimuth sensing device in the reference metrology unit, arranged to measure and store the value of the taut wire""s relative azimuth with respect to the reference metrology units horizontal axes (xr,yr);
a depth sensor arranged on the reference metrology unit for measuring the water depth dr;
that the base metrology unit is arranged to be carried by an ROV at a variable distance from the reference metrology unit and for aligned positioning at the second termination, with a relative azimuth sensing device arranged to measure and store the value of the taut wire""s relative azimuth xcex8B with respect to the base metrology units axes (xB,yB); and
transfer means for transmitting measured values from the reference metrology unit to the base metrology unit.
Advantages of the preferred embodiment will be explained in the detailed description of the preferred embodiment of the invention.